Rust-proofing process



Jan. 14, 1941. J, MacQUAlD v 2,228,336

' RUST-PROOFING PROCESS Filed May 25, 1936 2 Sheefs-Sheet 1 Jan. 14,1941. J. Ma'c uAm 2,228,836

RUST-PROQFING PROCESS Filed May 25, 1956 2 Sheets-Sheet 2 Patented 14,1941 PATENT OFFICE RUST-PROOFING rnocnss John mound, Detroit, Mich,assignor to General Motors Corporation, Detroit, Mich., a cor- Porationof Delaware Application May 25, 1936, Serial No. 81,632

4 Claims.

The invention relates to processes of applying rust-proofing solutionsto articles, more particularly those having a ferrous metal surface, toproduce thereon a coating tending to protect the iron or steel againstcorrosion or rust and adapted to retain other coatings, e. g., paint orenamel.

Methods of producing such rust-proof" coatings by treatment of thearticle with solutions adapted to deposit phosphates, chromates,oxalates, etc., have been known for many years, the use of zinc and ironphosphates with phosphoric acid being disclosed, for example, in patentsto Coslett 870,930 and 1,007,069, and oxalic acid in Gravell 1,315,017.The action of these baths was very slow and attempts were made to,expedite the process by addition of activating agents, one of the mostused being manganese compounds, as manganese dioxide. The time required,however, was still excessive, thirty to ninety min- 20 utes, one tothree hours or several hours being specified in patents dealing withsuch processes.

More recently there have come into general use other activating agentsthat still further ex- 25 pedite the reaction of rust-proofing chemicalswith the metal, such as chlorides, nitrates, nitrites, etc. The actionof these addition agents is variously explained, but the net effect asto time required for treatment has been such that,

in more recent practice, satisfactory coatings have been obtained byimmersionin hot baths for periods as short as three to ten minutes,depending somewhat upon temperature and con centration of the bath andthe amount of coating desired.

I have discovered that, irrespective of the type of rust-proofing bathemployed or of time-reducing chemical used, a further remarkableincrease in activity of bath or reaction velocity can be attained by anovel method of applying the solution to the surfaces to be treated. Inthe practice of this process, which may be properly described as thesurface scouring process, I apply the solution in continuous sheets orstreams to substantially all areas of the surface to be coated while thearticle is suspended in the air. This is accomplished in general bydirecting the solution in a large number of jets, preferablysubstantially at right angles to the surfaces to be treated, insufiicient quantity and at sufficiently high velocity to cause energeticwashing or scouring action upon the surfaces. This application of thesolution by what may be termed a blast 55 of solution and air iscontinued throughout the treatment period and .not merely to wet thesurface.

The powerful washing or scouring action may be appreciated from the factthat, in applying the process for example to an ordinary automo- 5 bilefender, solution is delivered at the rate of from four or five hundredgallons per minute up to twenty five hundred gallons or more per minuteinto a treating area of approximately eight feet in length under a pumppressure running as high as twenty pounds per square inch.

Typical rust-proofing solutions which I have employed in this processinclude, for example,

a solution adapted to produce a coating of chromate or chromates of ironupon ferrous metal surfaces and containing as its essential constituentschromic acid and an activating agent of the halogen type, as sodiumchloride. The proportions may vary widely but a typical commercial bathmay contain about two ounces of a mixture of chromic acid (C103) andsodium chloride (NaCl) per gallon of water. Another bath that may beemployed consists initially of a water solution of adihydrogen phosphateof zinc, iron or manganese or mixtures thereof with an activating agentof the nitrate type, e. g. copper or sodium nitrate. Still anothersuitable bath contains initially zinc dihydrogen phosphate activatedwith a nitrite or nitrous acid. It will be understood that the above aregiven merely as examples of suitable rust-proofing baths and are notintended as limiting my invention to use therewith since the inventioncontemplates the use of any chemical composition adapted to produce arust-proof or corrosion-retarding coating upon metal surfaces such asiron, zinc, magnesium, aluminum, etc., by reaction of the treatingchemicals with the metal of the surface.

In the prior use of rust-proofing solutions it has been the universalpractice commercially, so far as I am aware, to immerse the articles tobe treated in hot baths of the treating material. Some patents statethat the solution may be applied by brushing or spraying or immersion.The time required for treatment, however, and the small quantity ofsolution that could be made to remain on the surface by merely brushingor spraying the solution on the particle rendered such methods ofapplication inefiective for reaction, therefore, is increased byincreasing the rate of destruction of the chemical equilibrium towardwhich the reaction tends. To effect such result the waste products ofthe reaction should be removed as rapidly as possible from the metalsurface, which is the point at which the chemical action takes place. Inother words, the reaction takes place only at the actual surface of themetal or in the ionic layer contacting such surface. The reactionvelocity tends instantly to decrease in such layer in accordance withthe law of mass action. I therefore maintain a high reaction velocity byforcibly removing the mobile reaction products in the solution so as torenew rapidly the chemical unbalance upon which the reaction depends.

Among the reaction products hydrogen is usually an important factor. Ittends to form a sort of blanket on the metal surface which, in theimmersion process, is removed only by formation of bubbles and escapesfrom the bath by mere gravitational influences. Other products aresoluble or insoluble residues resulting from interaction of the metaland the acidic content of the bath but which do not enter into thecoating per se. The effect may be explained, in par-t, by 40 statingthat the surface of the metal becomes polarized and that furtherchemical or electrochemical action must await depolarization by removal,chemically or mechanically, of the polarizing agents. All of theseproducts are forcibly 45 removed by my process and a fresh supply ofchemicals is constantly brought to the reaction sphere, It may bepointed out that the purpose of spraying as hitherto suggested in theart was merely to get the solution on the surface,

50 whereas the basic idea in the present process is to get the solutionoff the surface and replenish the supply as rapidly as possible.

In practical application of the invention, 1 utilize apparatus one formof which is illustrated 55 in the accompanying drawings in which Figure1 is a side view, partly broken away, showing a treatment chamber andmechanism associated therewith.

Figure 2 is an end view of the same.

0 Figure 3 is a detail view of a nozzle structure that may be employed.

Referring to the drawings, 5 indicates a compartment which may be formedwith walls of sheet metal and of suitable dimensions to permit 65 thepassage therethrough of an article to be treated, for example a vehiclefender 6. End walls 1 and partitions 8 may be provided to hinder escapeof treating liquid and to define within the compartment a treatingchamber,

' 70 these walls and partitions being apertured to allow the articles topass through them. At the top-of the compartment is shown a conveyertrack or rail 9 on which trolleys it may travel, which trolleys areconnected and moved by a 75 chain ll. Hooks 42. are carried by thetrolleys aaaasae II from which may be suspended the articles to betreated. Shields I! are arranged on both sides of the conveyer chain andtrack to protect them from the treating chemicals.

Within the treating chamber defined by the partitions 8 are arrangedpipes ll, nine sets of which are shown. These are positioned upon bothsides of the path through which the articles 6 travel and, together withcross-headers l5, ai-

' most completely surround the said path. These pipes and headers may beconnected in any suitable manner, as by side-headers IE, to a riser ll,fed by the outlet of pump l8, driven by motor l9. Treating liquidcontained in reservoir 20 may be supplied to the pump through pipe 2|the entrance to which is screened by suitable filtering means 22.

Pipes l4 and I5 are provided with a large number of outlets arranged todirect jets of the treating liquid into the path of the article 6. Theseoutlets are preferably so constituted as to permit of adjusting thedirection of the jets, e. g., by universally adjustable nozzles 23, soas to enable the operator to obtain proper distribution of therust-proofing solution. In practice, with an article such as isillustrated, it has been found necessary to direct the nozzles, someforwardly, some rearwardly, and some to concentrate the jets toward theinner curved surfaces. The arrangement should be such that during atleast the major portion of the travel of the article through thetreating chamber, continuous blasts of liquid and the air necessarilyadmixed therewith will be directed toward all parts of the surface, thusmaintaining a continuous scouring and impact effect over the entiresurface.

The solution in the reservoir 20 may be maintained at any desiredtemperature by suitable heat-transfer medium in coils 24, a temperatureof approximately 180 F. being desirable for the rust-proofing solutionsin general use.

The length of the treating chamber and the rate of travel of theconveyer must, of course, be so coordinated as to efiect the desiredresult.

In other portions of compartment 5 outside the rust-proofing chamber orin adjoining compartments may be arranged means for preliminarilycleaning the metal surfaces and final washing. Apparatus of conventionalcharacter may be used to apply the cleaning and washing solutions. It

is highly desirable, however, that the washing step should followimmediately after the rustproofing treatment and before the surfacesdry, in order to remove at once the rust-proofing solution and preventspotting.

It will be noted that the eilect of the application of high-pressurestreams of solution to the metal surface will be to constantly wash fromthe surface the portions of the solution in which the active chemicalshave become partially depleted, in fact, a most energetic scouring andcleaning action is produced. At the same time, by using the solutionitself to efiect the scouring action, the initial concentration ofactive chemicals is constantly being restored, and with such impact asto promote by the actual pressure itself a most intimate contact of thechemical agents As a result of the effects above mentioned and possiblyother factors which have not yet been recognized or the nature andinfluence of which have not been understood, it has been found possibleto greatly reduce the time necessary for producing a satisfactorycoating. In actual commercial practice, chromate coatings are nowproduced in as little as fifty seconds as compared with several minutesin the best immersion procedure. With some of the more active solutionsthe time has been reduced to as low as twentyfive seconds for standardprocedure.

Further advantages of my process are found in the prevention of gaspockets and the avoidance of variations in chemical concentration ordistribution.

By proper arrangement and adjustment of the nozzles the liquid may be sodistributed and its impact and scouring effect upon the surfaces sodetermined as to substantially eliminate nonuniformity of coating andthe thin spots which have hitherto occurred in rust-proofingarticles ofirregular shapes. The reduction in time of .ing upon the articlecontinuously while in such chamber blasts of liquid and air at highvelocity, such liquid containing chemicals reacting with the metal toproduce upon the surface a corrosion-resisting coating and containingferrous salts, and so adjusting the blasts as to effect a substantiallyuniform coating upon the entire surface of the article.

2. Apparatus for rapidly producing a substantially uniformlycorrosion-resisting coating upon the surface of a metal articlecomprising a treatment chamber, means for supporting an article in theair, means for moving the article through the chamber, means formaintaining a supply of corrosion-resisting solution under highpressure, said solution containing ferrous salts and adapted to reactwith the metal surface to form a corrosion-resisting coating thereon,and means for directing upon the article while in said chamber blasts ofcorrosion-resisting solution and air at high velocity to therebyvigorously scour the surface of the article and rapidly form asubstantially uniform corrosion-resisting coating thereon.

3. Apparatus for rapidly producing a substantially uniformcorrosion-resisting coating on the surface of a metal article comprisinga substantially closed treatment chamber having an entrance and an exit,means for suspending the metal article to be treated in the air, meansfor moving said article through the treatment chamber, means formaintaining a supply of corrosionresisting solution under a pressure ofapproximately twenty pounds per square inch, said solution containingferrous salts and containing I chemicals adapted to react with the metalsurface to form a corrosion-resisting coating thereon, and means fordirecting upon the article while in said chamber blasts ofcorrosion-resisting solution and air at high velocity whereby thesurface of the article is vigorously scoured and a substantially uniformcorrosion-resisting coating rapidly formed on the article.

4. The surface scouring process of rapidly producing a substantiallyuniform corrosion-resisting coating upon the surface of a ferrous metalarticle comprising supporting the article in the air, continuouslydirecting upon the surface of the article while supported in the air ahigh velocity blast of rust-proofing solution admixed with air, saidsolution adapted to react with the ferrous metal surface to produce acorrosionresisting coating thereon and containing ferrous salts, andcontinuously washing away the mobile products of reaction by the highvelocity blast of rust-proofing solution and air.

JOHN MscQUAID.

